A radical compound is in highly activated state, so it has been customarily applied in various uses. For example, a radical initiator used as an initiator of polymerization in synthesis of polymer compound may be mentioned.
However, most radical compounds are unstable and destroy the radical state in the short period.
Among them, it is known that a nitroxy radical (>N—O−) is relatively stable and possible to maintain in radical state. For example, a compound having the nitroxy radical in molecule, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) is used as a spin labeling agent used for electron spin resonance analysis (ESR). In addition, this compound has been also studied for a medical application, and it is promised as a radiation protective agent used in cancer radiation therapy (e.g. see S. M. Halm, etc., “Evaluation of TEMPOL radioprotection in murine tumor model”, Free Rad. Biol. Med., 22, 1211-1216 (1997)).
Further, there is an organic radical polymer used in a non-aqueous electrolyte secondary cell, which was developed during developing remarkably in electronics in recent years and which would be expected in rapid charge/discharge (e.g. see JP2005-209498A).
The organic radical polymer performs as an active material of secondary cell and can achieve electrochemically a reversible oxidation-reduction reaction. In this oxidation-reduction reaction, when a nitrosonium (cation) is regulated by reversible electron exchange from outside between nitroxy radical and nitrosonium, the electron is emitted as counter anion and thus an electric current is induced.
A chromic compound has two different chemical species in a single compound and each of them has different light absorption wavelengths. So, it has a function to induce a reversibly structural isomerization between each species by external factors such as light, electricity and heat.
As a chromic compound, many compounds such as spiropyran and spirooxazine compounds are known (e.g. see the Chemical Society of Japan, Kikan Kagaku Sosetsu, No. 28 “Chemistry of Organic Photochromism”, P 70-88 (1996)). It is known also that these compounds are an organic compound which is synthesized in high latitude and that derivatives obtained from each group of these compounds can give different feature to the individual compound.
For example, since the spiropyran compound has a carbon-carbon double bond portion (—C═C—) acting as a chromophore in the pyran ring and the bond portion has a structure which is easily auto-oxidized by singlet oxygen, it is to say that the term maintaining durability of reversible isomerization of the compound is short.
The spirooxazine compound has a structure that the pyran ring of spiropyran compound is replaced with an oxazine ring and a carbon-nitrogen double bond portion (—C═N—), which is the chromophore on the oxazine ring, is attacked by singlet oxygen as the pyran ring of the spiropyran compound. However, because it is considered that the attack of the carbon-nitrogen double bond by singlet oxygen is difficult compared with the carbon-carbon double bond, its degradation by automatic oxidation becomes hard, and thus its durability of reversible isomerization is improved. Therefore, in the Spiro compound which exhibits chromic property with high repeating durability, spirooxazine compound is preferable, and for example, it is applied as a functional pigment.
In addition, the conventional spirooxazine compound directly introduced a group having radical, an instable chemical species, is not known, although the conventional spirooxazine compound introduced a stable substituent such as hydroxyl, alkyl, aryl, aralkyl, alkoxyalkyl, alkylcarbonyl, and alkoxycarbonylalkyl groups onto the nitrogen in the heterocyclic ring forming one side of the spiro ring such as indoline, thioline, and selenazoline rings are known (e.g. see the Chemical Society of Japan, Kikan Kagaku Sosetsu, No. 28 “Chemistry of Organic Photochromism”, P 70-88 (1996), JP 2000-026469A).
As a stable radical compound, some heterocyclic ring compounds having nitroxy radical group are present, and in addition to the above TEMPOL, spin adduct of 5,5-dimethyl-1-pyrroline-N-oxide, 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, 4-carbamoyl-2,2,6,6-tetramethylpiperidine-1-oxyl, 4-metacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl are known.
These heterocyclic ring compounds having stable nitroxy radical group change reversibly between nitroxy radical and nitrosonium ion when giving different potentials. In other words, they show reversible oxidation-reduction reaction and exchange of electrons occurs. However, for the reversible state change of oxidation-reduction reaction of organic radical compounds having a stable radical group such as nitroxy radical, there was no method to measure it other than direct measurement of the oxidation-reduction potential.
Consequently, an problem of the present invention is to provide new spirooxazine radical derivatives which exhibit chromic property, which has both stable radical group contributing to generation of oxidation-reduction reaction and chromophore contributing to the chromic property to control oxidation-reduction reaction of organic radical compounds by giving different wavelength light, can removes color change also in case that there is a change in absorption spectrum accompanied with photoisomerization and there is an absorption in visible range, and can identify the generated state of radical and cation species by difference of absorption wavelengths.